This invention relates to a motor controller which has a draw-out carriage assembly and more particularly to an interlock for preventing the carriage assembly from being racked-in or racked out when the main contactor is energized.
When the main contactor of a draw-out type circuit breaker is closed, racking the carriage assembly in or out will cause the stab assembly to make or break load current which can cause severe arcing and overheating of the stab assembly. It is therefore desirable to rack the carriage assembly in or out only when the main contactor is open which prevents severe arcing and overheating of the carriage stab assembly. The carriage assembly usually has a handle which has an "ON" position and an "OFF" position. In the "ON" position, the carriage assembly is racked-in and the stab assembly is engaged with the bus bars and in the "OFF" position, the carriage assembly is racked-out and the stab assembly is disengaged from the bus bars. The handle normally operates some mechanical linkage arrangement which affects the racking in and racking out of the carriage assembly.
U.S. Pat. Nos. 4,427,854 and 4,447,858 disclose motor control centers which have a draw-out type circuit breaker. A handle is attached to a bellcrank which translates the motion of the handle into a motion which racks the carriage assembly in and out connecting and disconnecting the stab assembly from the bus bars. The carriage assembly includes a lever which has a finger which engages notches in the bellcrank. When the contactor is opened, the lever is held away from the bellcrank so that the finger does not engage either notch and the carriage assembly can be moved in or out. When the carriage assembly is racked-in and the main contactor closes, the finger engages the first notch and the carriage assembly cannot be racked out until the main contactor is open. When the finger rides along the surface between the first and second notches, the main contactor is prevented from closing. In order to assure that circuit making and breaking is done only by the contactor elements, racking of an already closed contactor is prevented. With the contactor closed, the interlock lever is rotated clockwise so that the finger engages the second slot in the bellcrank. In this position, power is available to operate the contactor but the mechanism is arranged such that the carriage cannot be racked-in when the finger engages the second notch. While this interlock arrangement performs as designed, its performance is dependent upon the interlock lever being mechanically operated by a push bar which is connected or linked to the main contactor. It will be appreciated that where a vacuum contactor is used, there is no external moving part on which to connect such a bar. Accordingly, it will be appreciated that it would be highly desirable to provide a mechanical interlock which can be used with a vacuum contactor.
Accordingly, it is an object of the present invention to provide a mechanical interlock for preventing the racking-in and racking-out of the carriage assembly when the contactor is energized.
Another object of the invention is to provide a mechanical interlock which is free of mechanical connection to the moving parts of the vacuum contactor.